Control of both PM2.5 and O3 in Beijing-Tianjin-Hebei and the surrounding areas

Serious haze pollution (e.g., PM2.5, particulate matter with aerodynamic diameters less than 2.5 μm) and increased ground-level ozone are severe air quality issues in China. In Beijing-Tianjin-Hebei and the surrounding areas (denoted as BTH&SA), although recently the particulate matter pollution appeared to be under control due to stringent pollution mitigation measures, ozone pollution rebounded rapidly, especially during summers. Thus, the exploration of strategies for efficiently lowering both ground-level ozone and PM2.5 concentrations is urgently needed. In this study, we target on the precursors contributing to both ozone and PM2.5 formation (i.e., NOx and volatile organic compounds (VOCs)) and adopt a Combined Empirical Kinetics Modeling Approach (CEKMA) to synthetically evaluate the cost-effective mitigation strategies for air quality control. We find that over the BTH&SA region, the choice of mitigation strategy in the initial stage (e.g., within 20% reductions on NOx or VOCs emissions) is critical because NOx-focused strategies may exacerbate O3 pollution. In addition, equally reducing NOx and VOCs emissions may have the least benefit for air pollution improvement. From a long-term perspective, we suggest reducing VOCs emissions by ~60% and NOx emissions by ~20% in the first stage, thereby avoiding the potential increase in ambient O3. Then in the second stage, the remaining VOCs and NOx emissions should be phased out to reach a deep mitigation of PM2.5 and O3. With those steps, both PM2.5 and ozone can be mitigated efficiently over the BTH&SA region.